Expert Voices

Mars is littered with 15,694 pounds of human trash from 50 years of robotic exploration

shiny object on dark reddish surface
Rovers on Mars frequently come across debris, like this heat shield and spring, from their own or other missions. (Image credit: NASA/JPL-Caltech)

This article was originally published at The Conversation. (opens in new tab) The publication contributed the article to Space.com's Expert Voices: Op-Ed & Insights.

Cagri Kilic (opens in new tab), Postdoctoral Research Fellow in Robotics, West Virginia University

People have been exploring the surface of Mars for over 50 years (opens in new tab). According to the United Nations Office for Outer Space Affairs (opens in new tab), nations have sent 18 human-made objects to Mars (opens in new tab) over 14 separate missions. Many of these missions are still ongoing, but over the decades of Martian exploration, humankind has left behind many pieces of debris on the planet's surface.

I am a postdoctoral research fellow (opens in new tab) who studies ways to track Mars and moon rovers. In mid-August 2022, NASA confirmed that the Mars rover Perseverance had spotted a piece of trash jettisoned during its landing, this time a tangled mess of netting. And this is not the first time scientists have found trash on Mars. That's because there is a lot there.

Related: Mars rover Perseverance spots shiny silver litter on the Red Planet (photo)

All spacecraft that land on Mars eject equipment, like this protective shell, on their way to the Martian surface. (Image credit: NASA/JPL-Caltech)

Where does the debris come from?

Debris on Mars comes from three main sources: discarded hardware, inactive spacecraft and crashed spacecraft.

Every mission to the Martian surface requires a module (opens in new tab) that protects the spacecraft. This module includes a heat shield for when the craft passes through the planet's atmosphere and a parachute and landing hardware so that it can land softly.

The craft discards pieces of the module as it descends, and these pieces can land in different locations on the planet's surface — there may be a lower heat shield in one place and a parachute in another. When this debris crashes to the ground, it can break into smaller pieces, as happened during the Perseverance rover landing in 2021 (opens in new tab). These small pieces can then get blown around because of Martian winds.

The Perseverance rover came across this piece of netting on July 12, 2022, more than a year after landing on Mars. (Image credit: NASA/JPL-Caltech)

A lot of small, windblown trash has been found over the years — like the netting material (opens in new tab) found recently. Earlier in the year, on June 13, Perseverance rover spotted a large, shiny thermal blanket wedged in some rocks 1.25 miles (2 kilometers) from where the rover landed. Both Curiosity in 2012 (opens in new tab) and Opportunity in 2005 (opens in new tab) also came across debris from their landing vehicles.

The European Space Agency’s Schiaparelli lander crashed onto the surface of Mars in 2016, as seen in these photos of the crash site captured by NASA’s Mars Reconnaissance Orbiter. (Image credit: NASA/JPL-Caltech/Univ. of Arizona)

Dead and crashed spacecraft

The nine inactive spacecraft on the surface of Mars (opens in new tab) make up the next type of debris. These craft are the Mars 3 lander, Mars 6 lander, Viking 1 lander, Viking 2 lander, the Sojourner rover, the formerly lost Beagle 2 lander (opens in new tab), the Phoenix lander, the Spirit rover (opens in new tab) and the most recently deceased spacecraft, the Opportunity rover. Mostly intact, these might be better considered historical relics than trash.

Wear and tear take their toll on everything on the Martian surface. Some parts of Curiosity's aluminum wheels have broken off (opens in new tab) and are presumably scattered along the rover's track. Some of the litter is purposeful, with Perseverance having dropped a drill bit onto the surface (opens in new tab) in July 2021, allowing it to swap in a new, pristine bit (opens in new tab) so that it could keep collecting samples.

The wheels of the Curiosity rover have taken damage over the years, leaving behind small bits of aluminum. (Image credit: NASA/JPL-Caltech)

Crashed spacecraft and their pieces are another significant source of trash. At least two spacecraft have crashed, and an additional four have lost contact before or just after landing. Safely descending to the planet's surface is the hardest part of any Mars landing mission — and it doesn't always end well (opens in new tab).

When you add up the mass of all spacecraft that have ever been sent to Mars, you get about 22,000 pounds (9979 kilograms). Subtract the weight of the currently operational craft on the surface — 6,306 pounds (2,860 kg) — and you are left with 15,694 pounds (7,119 kg) of human debris on Mars.

Why does trash matter?

Today, the main concern scientists have about trash on Mars is the risk it poses to current and future missions. The Perseverance teams are documenting all debris they find and checking to see if any of it could contaminate the samples the rover is collecting. NASA engineers have also considered whether Perseverance could get tangled in debris from the landing but have concluded the risk is low (opens in new tab).

The real reason debris on Mars is important is because of its place in history. The spacecraft and their pieces are the early milestones for human planetary exploration.

This article is republished from The Conversation (opens in new tab) under a Creative Commons license. Read the original article (opens in new tab).

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Cagri Kilic
Postdoctoral Research Fellow in Robotics, West Virginia University

Kilic is a Postdoctoral Research Fellow in the WVU Navigation Laboratory (NavLab). During his Ph.D. studies, Kilic researched space robotics localization applications using terramechanics relations with inertial sensors. His current research focuses on computationally efficient and verifiable state-estimation techniques, emphasizing cooperative localization, perception and planning of aerial robots. Kilic is a past recipient of the Fulbright Scholarship, WVU Statler Fellowship and Caltech's NASA Jet Propulsion Laboratory JVSRP Fellowship.